Electrothermic process of treating high resistance material



Feb. 28, 1933. I. H. DERBY ELECTROTHERMIC PROCESS OF TREATING HIGHRESISTANCE MATERIAL Filed May 8, 1929 gmmatcw fl p e?) Patented Feb. 28,1933 UNITED STATES PATENT OFFICE IRA. H. DERBY, F INDIANAPOLIS, INDIANA,ASSIGNOR TO PETER C. REILLY, Q1? INDIANAPOLIS, INDIANA ELEGIBOTHEBMIOPROCESS OF TREATING HIGH RESISTANCE MATERIAL Application filed May a,

This invention relates to an electrothermic process of treating highresistance materials and is generally applicable to the treatment of anymaterial having high electrical resist- 5 ance and containingsubstantial amounts of volatile material.

One ap lication to which this process is particular y adapted is in thedrying or seasonin of green wood. Wood as it finds application in thearts and industries requires seasoning in order to remove the moisturewhich it contains .and to prevent its warping after it is in thefinished state. In its green and dry states wood is a very poorconductor of heat. When green it is a partial conductor of electricity,but when dry it is practically a non-conductor of electricity. Ordinarymethods of seasoning wood are necessarily slow processes due to thisproperty of poor heat conductivity.

In the usual airdrying process commonly known as seasoning, the moisturecontained in the wood slowl escapes by diffusion and transpiration, butof which processes are materially influenced by the" degree ofcomactness and porosity ofthe wood structure. uring ordinary dryingprocesses the outside surface of thewood dries first and shrinks,

forming a dense layer which is more or less' impervious to the moisturecontained in the inner layers of the wood. This case hardening processmaterially lengthens the time required for the wood to season andencourages crackin and warping which always occur unless the woodconditioning operations are carried out slowly, uniformly and with extreme care.

I have discovered that the dryin rocess can be materially shortened ifthe wfiolh body 40 of the woody material is raised to a temperaturesufiicient to evaporate the contained moisture and to establish a highvapor Velocity outwardly through the ducts and openings in the wood.Such a process which may be said to raise the temperature of-the entirebody equally or substantially so throughout,

. prevents case hardenin and accelerates the transpiration velocity trough the cell walls and t e woody tissue.

My process consists in establishing an elec- 1929. Serial R0. 381,524.

manner the electrical energy is largel converted into heat according tothe well own equation:

2 E H=KO RKC'EK (where H equals heat units; C equals current in amperes;R equals resistance in ohms; E equals electromotive force in volts; andK is a reduction factor). By this process the current may be regulatedproperly so as'to raise the temperature of the entire mass of materialto any desired degree, thereby causing the contained moisture to berapidly evaporated and expelled.

This process is also ap licable to bending, shaping or molding woo intovarious irregular forms. If it is desired to use green wood or partiallyseasoned wood the current is applied to the material until the containedmoisture is substantially removed by evapo ration and the-wood fibersare uniformly softened throu hout. When the entire mass is plastic andexible it may be shaped and held in any desired irregular shape. Aftershaping, the heating process may be continued until the material isentirely dry or the material may be held in its shaped osition while thetemperature is allowed to fill to normal. Ordinarily, the process ofshaping timbers is carried out b heating and softening the wood in steamor several hours before it is shaped or molded. .After. themoldingprocess it is then held in its new form and allowed to cool .and .dry.By my process the length of time required for such operations ismaterially reduced.

The accom anyingdrawing is a diagrammatic view s owing-one form ofapparatus which is well adapted for carrying out processes embodying myinvention. 100

Referring to this drawing, the reference character 1 designates asultable source of high voltage electricity, here shown as a generatorof the alternating current type, although a direct current source mayalso be used. This machine supplies current from brushes 2 through aswitch 3 to the primary P of a step-up transformer T. The secondary S ofthis transformer is connected to electrodes 7 by means of line wires 5and G. lVhen a unidirectional current is employed it is best obtained byrectifying the high voltage alternating current by any of the well knownmeans.

In carrying out the process, it is necessary that the electrodes befreely pervious to gases and vapors so as to allow their ready escapeand for this purpose electrodes 7 comprise a body portion ofelectrically conductive material carrying a series of metallic bristles8 covering'the entire surface thereof at closely spaced intervals. Eachof these electrodes is rigidly connected to a bank of insulators 1.0which are in turn attached to a supporting rod 12 having an enlargedhead 11 cooperating with a compression spring 14. Each rod 12 passesthrough an opening in a suitable support 15 and is normally urgedoutward from this opening by the action of spring 14. A nut and washer13 secured to the end of rod 12 prevent the electrode from being pushedentirely through the supports 15 byt-he re action of the'spring.

Mounted between the two electrodes 7 and contacting closely with theextendingends of bristles 8 is a block of material 9 to be treated. Ashere shown, this material is a wooden cross tie which is to beseasonedprior to impregnation with creosote oil or other preservative.It will be clear that electrodes 7 and tie 9 complete the secondarycircuit of transformer T, but that due. to the presence of the two banksof insulators 10, the current is confined to this circuit.

Although I have shown the electrodes 7 as carrying a series of metallicbristles 8, this particular structure is merely illustrative sincetheonly requirement is that each electrode shall contact with the highresistance material at a mat number of closely spaced points, and thatthe current pass through practically the entire cross sectional area of.

the material to be treated and cause a' temperature rise throughout thismaterial.

When this tic 9 is )laced in position between thetwoelectro es 7, thecompression springs 14 react between the stationary sup- .ports 15 andthe blocks ll'carried by rods 12, and force the bristles 8 into veryclose electrically conducting contact with the ends of the tie. When theswitch 3 is closed, high voltage alternating current is supplied tothese electrodes and circulates through the secondary circuit oftransformer T, this circuit being completed bythe cross tie 9. The

'tically the entire surface.

ti-e 9 may be Wei hed prior to the starting of the rocess and it may beremoved and weig ed at suitable intervals during the process, in orderto determine defi itely when the desired condition of the tie isreached. After the length of time required has been determined bytreating several ties, the approximate time required will be known andthen the weighing process may be dispensed with. I

In preparing ties for use by railroads, 'such ties are commonlysubjected to a long air seasoning process throughou a period of twelveto eighteen months. During this time between 20% and 30% of the originalweight of the wood is lost due to evaporation of the contained moisture,and the wood develops deep cracks and checks over prac- After theseasoning process, the wood is impregnated with creosote oil or otherpreservative. By the use of my process the time re uired for thistreatment may be reduced to hours as compared with months by the formerprocess.

1 have found that in the creosotmg of ties my process may beadvantageously carried out in the followin manner: An oak tie havingdimensions 0 7 by 9" by 8 has atotal overall electrical resistancebetween its ends of between 15,000 and 25,000 ohms and has a weight ofbetween 250 and 300 pounds. If a current of between 1 and 2 amperes isapplied at a potential difference of between 15,000 and 50,000 volts,the temperature of the whole tie can be brought to the boiling point ofwater in about 5 minutes and may then be subsequently carried higher ifdesired, so that a considerable steam pressure is developed inside ofthe wood causing the water to rapidly distill away and the wood to dryin a veryshort time. The steam under; pressure esca es through the poresof the wood, carrying with it the enclosed gases and air, and after theprocess is complete the wood is relatively free from cracks or checkswhich result from .drying by most other processes. When the and leftuntil sufficient preservatlve has been absorbed. Condensation of thesteam in the wood'as the temperature falls, causes an effective pressureamounting approximately to one atmosphere when the W0 reachesatmospheric temperature, and this pressure forces the oil into the woodquickly and effectively; This absorption process may be carried outunder atmospheric pressure, or at a higher pressure if it is desired.

Some woods, such for example as white oak, hemlock, Douglas fir, arevery difiicult to treat with preservative or fire-proofing materialbecause of their slight porosity; These woods resist treatment becausethe pores or ducts through which the oil enters the wood in the moreeasily treated species, are plugged by tyloses and it is not possible toapply an external pressure sufiicient to force the oil into the woodwithout physical injury to the wood structure. By my process of heatingand seasonin it is possible to develop in the wood a higi internal steamand gas pressure which disrupts the tylose plugs and thus renders thewood porous, so that it can be readily impregnated with preservative orfire-proofing material.

To preventgross disruption of the wood by the high internal pressuredevelo ed in the heating I may place the electro es on opposite sides ofthe timber and sup ort them to resist the splitting of the woo byinternal pressure. The other sides may be held between insulatingretaining blocks. In the case-of cross ties or similar timber, otherties or timbers may be employed as insulating retainers. In thisoperation the wood is heated by the electric current across the rain.The ends are thus exposed for the ree exit of the steam and gases asthey escape from the interior of the wood following the disruption ofthe tylose plugs, or other duct obstructing formations.

I have referred to the use of an electrical potential difference of theorder of from '15,000 to 50,000 volts and by this I mean to imply thatthe exact potential difference employed is subject to considerablevariation,

- epending upon the condition and properties of the matter beingtreated. This process can be carried out by the use of eitherdirectcurrent or alternating current, and in the case of alternating currentthe frequency may be of any value which produces efiective heating ofthe material to be treated.

I have discovered that woody material dried in this manner is not onlyrelatively free fromcracks and checks, but is otherwise more durablethan when dried by other processes. The electricity appears to exercisea preserving action on the woody fibers so that they are more resistantto moisture and decay.

What is claimed is:

1. The process of treating woody material containing volatile matter,which consists in establishing an electrical potential difference of theorder or from 15,000 to' 50,000 volts between op osite faces of a bodyofsuch material, unti the temperature is such as to drive off the volatilematter.

2. The process of treating wood containing duct obstructingformationsand volatile matter,which c 6ns1sts in establishing a high difference ofelectrical potential of the order of several thousand volts betweenopposite faces of a body of wood, and maintaining such potentialdifference until the rise in temperature causes the duct obstructingformations to be removed and the moisture to be ex elled.

3. The process of drying a mass 0 wood in natural state, which consistsin applying and maintaining without 'arc discharge, a

potential difference of the order of several thousand volts to oppositefaces of the mass at a current density sufiicient to raise thetemperature of the wood to the evaporation point of the moistu retherein, and continuing such application until the pressure and steamgenerated expel the duct obstructing formations in the wood and driveoff the moisture contained in the wood cells.

4. The process of treating a mass of wood in its natural state, whichconsists in applying a potential difference of at least several thousandvolts to opposite faces of the mass and regulating such voltage toobtain a current density sufficient to raise the temperature of the masstothe evaporation point of the moisture therein, and continuing suchappli: cation to obtain evaporation in the wood cells and to expel theduct obstructing formations in the wood and drive off the moisture andva or by expiration.

n testimony whereof I have signed my name to this specification.

IRA H. DERBY.

CERTIFICATE or CORRECTION.

Patent No. 1,899,233. February 28', 1933.

IRA n. DERBY.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,line 52, claim 1, for "or" read-"of"; and that 'the said Letters Patentshould be read with this correction therein that the same may conform tothe record of the case in the Patent Office.

Signed and sealed this-28th day ot- March, A. D. 1933.

M. Moore, (Seal) Acting Commissioner of Patents.

